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Spring is Arriving Earlier and Earlier in the U.S.

A map showing how many days earlier "first leaf" is occurring in each U.S. state when comparing 1991-2010 with 1961-1980.

Today, March 20th, marks the first day of the vernal equinox, although spring might feel like it's never going to arrive for those still battling unseasonably cold weather from the Midwest to the East. But don’t be fooled by this year's cooler temperatures. When you define the onset of spring as the “first leaf” date for a number of plants, the season is arriving earlier, on average, than it did 30 years ago.

As a whole, the continental U.S. is seeing spring arrive three days sooner when you compare the period of 1991-2010 to 1961-1980 with a temperature data index developed by Mark D. Schwartz, a researcher at the University of Wisconsin-Milwaukee, and the U.S. National Phenology Network. The national average for the first leaf date is currently March 17, though this year buds on the East Coast may still be in hiding thanks to cooler-than-normal temperatures so far this month.

Regionally, there are even more dramatic changes. Parts of the Southwest and Southeast are seeing spring arrive up to a week earlier, while areas in the Northeast and Mid-Atlantic are experiencing spring five days earlier. New Mexico is leading the way state-wise, with spring starting an average of eight days earlier. Ohio, West Virginia, and Florida are the only outliers that have seen barely any change in the start date.

The shift toward an earlier spring is consistent with global patterns of climate change. Changes in first leaf date don't just pose an issue for gardeners. They have a trickle-down effect on animals also rely on these cues to lose their winter coats, prepare summer dens, give birth, and many other processes. While some might welcome a quicker exit from winter, it’s possible that these changes could disrupt delicate balances that have been in place for hundreds and thousands of years.

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